Ascending Aorta Outflow Graft Location and Pulsatile Ventricular Assist Provide Optimal Hemodynamic Support in an Adult Mock Circulation

Abstract

Although continuous flow (CF) and pulsatile flow (PF) ventricular assist devices (VADs) are being clinically used, their effects on aortic blood flow, as a measure of overall blood distribution, remain unclear. In acute VAD support animal experiments, our group has described a zone of turbulent mixing in the aortic arch. The objective of this study was to confirm this finding in the controlled setting of an adult mock circulation, simulating ventricular pathophysiologic states (normal and failing ventricle). CF and PF flow VADs were connected to ventricular apical inflow and ascending aorta (AA) or descending aorta (DA) outflow cannulae. Cardiovascular pressure and flow waveforms were recorded at varying levels of VAD bypass resulting in four test conditions: (i) CF-AA; (ii) CF-DA; (iii) PF-AA; and (iv) PF-DA. Confirming the animal data, no differences in mean aortic flow between CF and PF VADs were found, and significantly lower mean aortic arch flow with DA cannulation was noted. Mean aortic root flow decreased with increasing VAD bypass flow. As in the animal studies, despite similar mean flow rates, significant differences in waveform morphology were observed for AA and DA outflow graft locations and varying levels of VAD bypass. At 100% VAD support in the failing heart, PF restored waveform pulsatility to normal baseline while CF resulted in little pulsatility. These results confirm our earlier findings in the animal model, suggesting that outflow graft location may have a significant effect on aortic blood flow distribution. The long-term implications of these findings are being examined in ongoing studies.

Numerical simulation of cardiovascular dynamics with different types of VAD assistance

“…Previous research indicated that for VAD inlet cannulation the left ventricle cannulation configuration would be preferable, as it allows for more blood to be drained into the VAD thus reducing the work of the native ventricle (Tevaearai et al, 2001). The ascending aorta outflow configuration is better suited for outlet cannulation than the descending aorta configuration in maintaining aortic blood flow characteristics (Litwak et al, 2005). Thus in the current simulation for the in parallel VAD connection, the VAD inlet is connected to the left ventricular apex and the outlet to the ascending aorta.…”

“…Litwak et al (2004) examined the effect of constant flow and pulsatile flow VAD support and outflow graft location on aortic flow in an acute calf model. Litwak et al (2005) and Koenig et al (2004) conducted similar research in an adult mock circulation test rig. No differences in mean aortic flow between constant flow and pulsatile flow VADs were observed in their experimental results.…”

Ventricular Assist Device Outflow-Graft Site: Effect on Myocardial Blood Flow

“…Kar and colleagues [14] reported that LVADs implanted with an outflow-graft anastomosis to the descending aorta have potential drawbacks such as aortic valve fusion and aortic-root flow stagnation that may alter myocardial perfusion. Similarly, in their experimental study, Litwak and colleagues [16] reported that the mean aortic-arch blood flow decreased when the LVAD outflow-graft anastomosis site was the descending aorta versus the ascending aorta. They also reported that although mean aortic-root and carotid-artery flow are independent of the LVAD outflow-graft location, competitive flow between the native heart and the LVAD may result in turbulent mixing or stagnation in the aortic arch if the LVAD outflow-graft anastomosis is located in the descending aorta [16].…”

“…Similarly, in their experimental study, Litwak and colleagues [16] reported that the mean aortic-arch blood flow decreased when the LVAD outflow-graft anastomosis site was the descending aorta versus the ascending aorta. They also reported that although mean aortic-root and carotid-artery flow are independent of the LVAD outflow-graft location, competitive flow between the native heart and the LVAD may result in turbulent mixing or stagnation in the aortic arch if the LVAD outflow-graft anastomosis is located in the descending aorta [16]. Therefore, they suggested that anastomosis of the outflow-graft to the ascending aorta may be optimal for a continuous-flow LVAD.…”

A naturally shaped silicone ventricle evaluated in a mock circulation loop: A preliminary study

“…Flexible sacs have been used to create mock ventricles for use in mock circulation loops in previous studies [5,[12][13][14][15][16]. These mock ventricles were hemi-ellipsoid in shape rather than having the shape of a true ventricle, and thus flow patterns experienced in these ventricles are not indicative of the natural heart.…”